The company has also announced the Sleep Stages tool to analyze light, deep and REM sleep, and Sleep Insights to provide guidance to help improve your sleep.

The Fitbit Alta HR activity tracker has been unveiled as the world's slimmest wrist-based, continuous heart rate tracking device. It combines the benefits of Fitbit's PurePulse heart rate technology, automatic exercise recognition, sleep tracking, battery life of up to seven days and smart notifications in a "slim, versatile design that is easily customized to fit your style."

In order to cram the heart rate sensor in Alta HR, Fitbit developed a new chip that reduced the size and number of components needed, achieving a 25% slimmer design than Fitbit Charge 2. Rest of the "standard for Fitbit" features remain in place, including Reminders to Move, notifications, and SmartTrack automatic exercise tracking for activities like walking, running, cycling, elliptical, sports and aerobic workouts in the Fitbit app.

Also worth noting are the two new sleep tracking and improvement tools, Sleep Stages and Sleep Insights. The former utilizes accelerometer data and heart rate variability to estimate the amount of time you spend in light, deep and REM sleep, as well as time awake each night, to better understand your sleep quality. On the other hand, the Sleep Insights uses the whole of your Fitbit data to provide personalized guidance on how to improve your sleep for better overall health.

The two tools were developed with Fitbit's panel of sleep experts over the last two years, including Dr. Michael Grandner, director of Sleep and Health Research Program at the University of Arizona; Dr. Allison Siebern, consulting assistant professor at Stanford University Sleep Medicine Center, and director of Sleep Health Integrative Program at Fayetteville VA Medical Center; and Dr. Michael T. Smith, Jr., professor of Psychiatry, Neurology and Nursing, Johns Hopkins University School of Medicine.

"Alta HR and these powerful new sleep features demonstrate our continued focus on evolving our innovative technology to deliver deeper, more actionable insights to help our users improve their health," James Park, co-founder and CEO of Fitbit, said in a statement. "The miniaturization of our PurePulse heart rate technology opens up exciting opportunities for future generations of devices and new form factors. Our advances in sleep will provide millions of users around the globe accessibility to invaluable insights that previously could be obtained only through expensive lab tests."

Alta HR is available for presale today on Fitbit.com for $149.95. In early April 2017, Alta HR will be available online and in stores worldwide, including major North American retailers such as Amazon.com, Best Buy, Dick's Sporting Goods, Kohl's, Macy's, Nordstrom, Target, REI and Verizon.

Sleep Stages and Sleep Insights will be available globally in Spring 2017. The former will work with Alta HR, Blaze and Charge 2 devices via the Fitbit app on Android, iOS and Windows, and on Fitbit.com in the online dashboard; the latter will sing along all Fitbit devices that track sleep via the Fitbit app.